Class-I: Class I HDACs share homology with the yeast Rpd3. This class includes HDACs 1, 2, 3, and 8, and its members are expressed ubiquitously in humans. Members 1, 2, and 3 are found in multi-protein repressor complexes in the nucleus, where they regulate gene expression. HDAC8 is found in both the nucleus and cytoplasm, and while it has not been found in any multi-protein complexes, it has been described to be involved in transcriptional repression. (1)